The following U.S. Patents are believed to represent the current state of the art:
6,100,5386,107,9945,914,7095,977,8676,005,5566,031,5195,863,1135,748,1835,748,5125,767,8424,553,8424,688,9334,782,3285,502,5145,633,6915,831,6015,786,8105,909,2105,880,7125,736,9765,818,3615,867,1465,785,4395,577,8485,793,3585,595,4495,581,4846,104,3845,748,5125,821,9225,864,3346,094,1965,936,6155,835,0946,097,3755,933,1325,986,2615,705,8785,677,978
The following patent documents are believed to be most relevant to the present invention:    U.S. Pat. Nos. 5,734,375; 5,736,976; 5,767,842; 6,031,519; 6,043,805 and Published PCT Patent Application WO 00/21024.